Are broadleaf herbicides effective when applied during dry weather?
Broadleaf herbicides are most effective when applied to weeds that are actively growing. During prolonged periods of dry weather, some weeds are likely to curl up or wilt. An application of a broadleaf herbicide to drought stressed weeds will likely be less effective as wilted foliage will absorb less herbicide than healthy foliage.
Broadleaf herbicides can be applied from mid-September to early November in Iowa. In dry fall weather, wait for a good rain or irrigate the lawn before applying a broadleaf herbicide. One-half inch or more of water (either from rainfall or irrigation) will quickly revive most drought stressed weeds.